Use text nibs

Hopefully this doesn't break anything (nothing I could see), but the playlist.nib was troublesome. After each language conversion xcode would crash and randomly modify other resources. After a painful process compilation warns about the Korean version of playlist.xib:

    /* com.apple.ibtool.document.notices */
    /Users/gradha/project/Movist/Resources/Korean.lproj/Playlist.xib:24: note: View is clipping its content
    /* com.apple.ibtool.document.warnings */
    /Users/gradha/project/Movist/Resources/Korean.lproj/Playlist.xib:5: warning: Content rectangle not entirely on screen with the menu bar (May not be completely visible for all screen resolutions and configurations)

I also moved resources to a subdirectory to follow the logical folder tree in xcode and avoid root clutter.